Creation and maintenance of aseptic conditions is a very important requirement in many scientific, medical and commercial activities. Sterilization of material, vessels and tools is an important task when these are to be used in biological or medical applications. Today, when the awareness to clean environment and clean work is higher, the importance of clean and sterile tools is a trivial prerequisite when surgical equipments are concerned. Laboratories for medical work or for biological research and development need to work in sterile conditions. Any medical equipment has to be sterilized prior to its use. Dental and hairdressers tools may transfer sources of infection and should therefore be sterilized every time before use. Vessels and tools for tissue culture work have to be sterilized to provide appropriate aseptic environment required for tissue culture applications. The plant tissue itself must also be sterilized before the propagation process can be started. Sterilization of medical tools such as endoscopes and other optical tools for medical examination imposes problems related to effective cleaning of the tools in a short period. The sterilization methods known today include heating, chemical disinfection, UV rays and nuclear radiation. Heating in an autoclave has been the most commonly used procedure because of its availability and application simplicity. However, high temperatures and pressures associated with steam autoclaving place very stringent property specifications on materials for vessels and tools. The sterilization of some materials by heat, particularly plastics, is very limited. Sterilization of devices which include optical and electronic components, which are not "autoclavable" is also problematic. Chemical sterilization techniques are commonly available, but these are usually limited by toxic residues, and require safety precautions for human laborers. Other difficulties that may be encountered with chemicals are special regulations for application and storage of potentially hazardous chemicals. In R&D laboratory work the chemical sterilization can also affect scientific experiments in an adverse way by its residual influence mainly on biological matter. UV and other radiation techniques generally require special instruments that are not commonly available. Nuclear radiation is very effective but it can only be done in special installations. People are often reluctant to use it and it can not be used to sterilize living plant material. Therefore "cold" sterilization techniques with minimal toxicity are highly desirable.
One potential sterilization technology is ozone sterilization. The ozone is a gas produced on site by high voltage gas discharge or by ultraviolet radiation.
Ozone sterilization has become a widely used technique for purification of municipal water systems, particularly from bacteria. The use of ozone generator in swimming pool water treatment is very common. It is also used for sterilization of medical equipment and in the food industry. These commercial applications suggest that ozone sterilization might be viewed as a potential alternative for asepsis purposes. Advantages are simplicity of application, flexibility in operation, minimal toxic residue and relatively low costs. There is no need for raw material which is readily available anywhere and almost no temperature differences are present. It will enable sterilization of a wide range of materials for equipment, tools and growing vessels.
The conventional known technique for atmospheric and surface ozone sterilization is to use a remote, high voltage discharge ozone generator (ozonator) from which ozonized air is directed to a closed vessel holding the substance to be sterilized.
Since ozone is an unstable gas, its concentration is reduced rapidly along its way to the point of application. Thus, in order to get the required concentration at the application point, relatively large ozonators must be used. Larger ozonators require higher electric power and better electric insulation measures. The higher concentration of the ozone at the source calls for more precise sealings. The conventional method is more suitable for large scale sterilization in relatively big chambers where many parts are sterilized together. This conventional method is not very effective in sterilizing surfaces which are not readily exposed to the Ozone. Sterilization of encapsulated objects is not effective at all. After sterilization, the sterilized object has to be removed from the sterilization chamber. By the mere opening of the chamber, new infection may be caused if no special precautions are met.
Another known method is used only in very large volumes by placing the ozone generator inside the large (technological) vessel. In this case, the internal surface and the whole volume are exposed to infection while the generator is being removed. For this reason the method did not become widely used for general purposes.